Pressure signal operated switches are well-known. It is also well-known to use a number of such pressure switches in combination, arranged to open or close electrical circuits in response to different pressure levels from a single source of pressure. The use of multiple switches is not suitable in some installations because it requires the availability of multiple suitable mounting locations for the switches, one for each switch, multiple taps into the pressure system, and multiple conduits leading from the tap points to the switches. In installations in which there are fewer suitable mounting locations for pressure switches and/or fewer suitable tap points than there are functions to be controlled by a pressure signal, multiple switches either cannot be used or require undesirable compromises in order to make their use possible. For example, in many vehicle air-conditioning systems it is desirable to have a multimodal response to the compressor head pressures but there is generally only one suitable mounting location for a pressure switch. This has led to the undesirable compromise of locating one pressure switch in the suitable protected location and locating the other pressure switch or switches in locations in which the switches are insufficiently protected from the environment. The unprotected switches are subject to destructive environmental influences that can lead to early failure and to an overall lessening of reliability.
An object of the present invention is to provide a single switch mechanism that requires only a single mounting location and a single tap-in point and that is adapted to perform plural switching functions in response to variations in a single pressure signal. It is further an object of the present invention to provide such a switch mechanism that is suitable for use in vehicle air-conditioning systems, including those in which there is only one suitable protected mounting location for a pressure switch.
In certain applications that require a multifunction switch mechanism responsive to a single variable pressure signal, the normal operation of the system requiring the switch mechanism involves the regular cycling of the pressure signal between pressure levels. For example, in some vehicle air-conditioning systems an auxiliary cooling mechanism for the condenser is provided to be operational when the pressure in the compressor reaches a certain level and to cease operation when the pressure drops below a certain level. It is desirable to reduce the regular cycling frequency of such a mechanism in order to avoid wear of and the noise caused by the auxiliary cooling mechanism, to save energy and to avoid wear of the switch mechanism itself. Therefore, it is another object of the present invention to provide a multimodal pressure switch that has an increased differential range to reduce the frequency of the regular cycling.
If the pressure can not be reduced by the auxiliary cooling mechanism and the pressure continues to rise, it is necessary to turn the compressor off to prevent damage. It is imperative that the pressure drop back down to the normal range before the compressor is started again or clutch failure may result. Therefore, it is desirable to provide a time delay or differential range between deactivation and reactivation of the compressor that is sufficiently large to ensure that the pressure is in the normal range before the compressor is reactivated. Such a differential range will reduce wear of the compressor and the clutch. Hence, it is still another object of the present invention to provide a multimodal pressure switch that has such a differential range.
The patent literature includes numerous known switches and switch systems. Of particular interest is U.S. Pat. No. 4,048,455, granted Sept. 13, 1977, to Alan K. Forsythe and Charles J. Green. This patent discloses a multifunction pressure switch with a pivotal conduction plate.
The above patent and the prior art that is discussed and/or cited therein should be studied for the purpose of putting the present invention into proper perspective relative to the prior art.